This invention relates to an output split-type mechanical and hydraulic power transmission.
More particularly, this invention relates to an output split-type mechanical and hydraulic power transmission having a plurality of input-output speed ratio ranges.
In a conventional output split-type mechanical and hydraulic transmission utilizing a single input-output speed ratio range, the required horsepower capacity for a hydraulic pump motor used in the transmission is large. Because of this, conventional transmissions of this type are severely limited in a practical sense, i.e., the transmission is extremely expensive to manufacture, is large in size, and has a low power efficiency.
To attain the wide variation of speed changes required in automotive vehicles, conventional power transmissions have used a plurality of input-output speed ratio ranges. However, even when output split-type mechanical and hydraulic transmissions have incorporated the use of a plurality of input-output speed ratio ranges, no completely satisfactory results have been achieved and numerous problems have been encountered in meeting the necessary conditions and requirements.
In an output split-type mechanical and hydraulic transmission utilizing a plurality of input-output speed ratio ranges, it is desirable that the required horsepower capacity for the hydraulic pump motor be maintained at approximately the same level as the maximum output of the prime mover. To accomplish this, a transmission with a speed ratio varying from 0 to 1.0 should be divided into first and second input-output speed ratio ranges. When a transmission of this type is divided into first and second input-output speed ratio ranges, it is desirable to employ a pair of hydraulic pump motors, each having a horsepower capacity equivalent to the other, and a reaction shaft attached to one of the hydraulic pump motors rotatably changing in relationship to variation in the hydraulic capacity of the other of the hydraulic pump motors from a positive to a negative maximum.
In a transmission employing a pair of hydraulic pump motors as described above, to achieve the speed ratio variations, conventional practice would be to provide a differential gear mechanism exclusively for the first speed range having a standard speed ratio obtained during the middle of the first speed range and a differential gear mechanism exclusively for the second speed range having a standard speed ratio obtained during the middle of the second speed range. In this conventional practice, the input shafts of both the differential gear mechanisms are directly connected to the input shaft of the transmission so that the reaction shafts of both the differential gear mechanisms are negatively rotated to each other at the borders of the two speed ranges. It therefore becomes necessary to connect an additional mechanism between the two differential gear mechanisms to smoothly change the transmission from one speed range to the other. This structural arrangement of the transmission is complicated, is large in size, and makes the rotational speeds of the components of the differential gear mechanisms high during the second speed range, a range which is most frequently used during operation of the transmission.
Another conventional arrangement of the differential gear mechanisms, as an alternative to the above, would be to provide the differential gear mechanism exclusively for the second speed range having a standard speed ratio enlarged and a speed reducing mechanism interposed between the input shaft of the transmission and the input shaft of this differential gear mechanism. However, even in this arrangement, the speed-reducing ratio of the speed-reducing mechanism is large and thus continues to create problems of durability and noise during the more frequently used second speed range.
Numerous problems remain and no completely satisfactory results previously have been achieved. it is necessary that an output split-type mechanical and hydraulic transmission not only employ a plurality of input-output speed ratio ranges but also be small in size and low in manufacturing cost, have maximum power efficiency, and allow a high degree of design flexibility to meet the input-output speed ratio range requirements.
Accordingly, it is a primary object of this invention to provide a new and improved output split-type mechanical and hydraulic transmission employing a plurality of input-output speed ratio ranges.
It is a further object of this invention to provide a new and improved output split-type mechanical and hydraulic transmission having a high degree of design flexibility for establishing the plurality of input-output speed ratio ranges in accordance with predetermined operational requirements.
Another object of this invention is to provide a new and improved transmission of the above-described type wherein each input-output speed ratio range is continuous to make possible a continuous variable drive ratio.
Another object of this invention is to provide a new and improved transmission of the above-described type which has clutch means for selectively connecting components of the differential gear mechanisms with the input and output shafts and the hydraulic pump motors for establishing the plurality of input-output speed ratio ranges, thus minimizing the transmission size, and the weight and manufacturing cost of the transmission.
Still another object of this invention is to provide a new and improved transmission of the above-described type wherein the components of the differential gear mechanisms have rotational speeds maintained within practical operational limitations thereof.
A further object of this invention is to provide a new and improved transmission of the above-described type which arranges the differential gear mechanisms and rotational shafts of the hydraulic pump motors coaxially or in parallel with the input and output shafts.
Finally, it is an object of this invention to provide a highly simplified output split-type mechanical and hydraulic transmission which is small in size and low in weight and manufacturing cost, while transmitting maximum and continuous drive power.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the output split-type mechanical and hydraulic transmission of this invention comprises: (1) an input shaft; (2) an output shaft; (3) first and second hydraulic pump motors hydraulically connected to each other, and at least the first pump motor having a variable hydraulic capacity and being mechanically connected to the input shaft; (4) a first differential gear mechanism including at least three elements, the first element being connected to the input shaft, the second element being connected to the output shaft, and the third element being connected to the second pump motor; (5) a second differential gear mechanism including at least three elements, the first element being connected to the input shaft, the second element being connected to the output shaft, and the third element being connected to the second pump motor; and (6) clutch means for selectively cooperating with the elements of the first and second differential gear mechanisms to establish different input-output speed ratio ranges, the clutch means including clutch means for selectively connecting the second element of the second differential gear mechanism to be output shaft.
It is preferred that the first differential gear mechanism of the output split-type mechanical and hydraulic transmission comprise a first planetary gear having a first sun gear connected to the second pump motor, a first ring gear connected to the input shaft, a first pinion meshed with the first ring and sun gears, and a first carrier rotatably supporting the first pinion and connected to the output shaft.
It is further preferred that the second differential gear mechanism of the output split-type mechanical and hydraulic transmission comprise a second planetary gear having a second sun gear connected to the input shaft, a second ring gear connected to the second pump motor, a second pinion meshed with the second ring and sun gears, and a second carrier rotatably supporting the second pinion and connected to the output shaft.
Finally, it is preferred that the output split-type mechanical and hydraulic transmission have the output shaft coaxially arranged with the input shaft, the first differential gear mechanism coaxially arranged with the input and output shafts, and the hydraulic pump motors including rotational shafts parallel to the input shaft.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention.